The anthropological literature on primitive legal systems has attracted considerable attention from economists in recent years. These systems are of interest because they apparently represent examples of law and order without a state government (Posner 1980, 1981). Economic theory explains human behavior by considering how individuals react to incentives and constraints in various institutional settings, and the following examination will emphasize institutions and incentives which influence legal evolution. Such an economic perspective has been applied to primitive legal systems by Demsetz (1967) who explained the incentives to establish property rights and applied his analysis with examples from American Indian history. Johnsen (1986) explored the consequences of such incentives for the formation and protection of property rights among the Kwakiutl Indians. Similarly, Baden et al. (1981) examined the resource management incentives of various American Indian tribes. The presentation below extends these studies by emphasizing the process and institutions of legal change (property right formation and change) in order to focus on an argument recently resurrected by Posner (1980, 1981). Posner clearly demonstrated that examination of primitive legal systems from the perspective provided by the economic approach reveals that formal institutions of government are not needed in order to have a system of effective law and law enforcement. However, he emphasized the “customary” character of primitive law and described it as a “complex, slowly changing system of exact rules” (1981, p. 178). Indeed, Posner maintained that primitive law had no means of changing rules quickly.